Thermostat



March 24, 1953 w. H. GlLLE 2,632,797

THERMOSTAT Filed Feb. 16, 1949 2 SHEETSSHEET l INVENTOR. wlLLlS H. GiLLEBY aw H TTORNE'Y Patented Mar. 24, 1953 UNITED STATES PATENT OFFICETHERMOSTAT Willis H. Gills, St. Paul, Minn, assignor toMinneapolis-.lloneywell Regulator Company, Minneapolis, lliinn., acorporation of Delaware Application February 16, 19.49, Serial No.76,313:

(Cl. HES-+320) 8 Claims.

The present invention relates to thermostats control that is not soequipped. Modern thermo-.

stats-of this type are so constructed as to re-.- quire a definitedifferential of temperatures to actuate the controlling means between onand off positions and thereby obtain positive on and oil operation ofthe heating device. If the thermostat is not equipped with ananticipating heaterthe heating device, once there has been a call forheat, will operate to heat up the furnace or boiler before heat will besupplied to the space and will continue to raise the furnace or boilertemperature while the space is being heated to actuate the thermostatthrough its operating di-fferentia 1. Then when the thermo-.. stat issatisfied, unwanted heat will be supplied; to the space before thefurnace or boiler cools. down. This difficulty is largely eliminatedwhen the thermostat is provided with a heaterfor supplying artificialheat to the thermal element as soon as the heating cycle begins.

An anticipating heater should be so disposed with respect to the thermalelement and of proper resistance so that Whenenergized by theavailablecurrent it will raise the temperature of the thermal element by anamountslightly more than the amount of the operating differe n tial ofthe thermostat. The heat supplied by the anticipating thermostat iscritical. It too much heat is supplied the control point of thethermostat will be undesirably reduced during cold weather whencontinued operation-of the furnace or boiler is required since theanticipating heater also will. be energized a large portion of the time.Also in mild weather, excessiveheat supplied by the anticipating heaterwill result in undesirably short operating periodsof the fur.- nace orboiler. If too littleartificial heat is. supplied to the thermal elementthe advantagesof the anticipating heater are lost inthat exeese siveheat will be supplied to the space being.- heated after the thermostatis satisfied, and the system will overshoot in mild Weather.

In the usual thermostat theanticipating heater is connected in serieswith control contacts and theothermost ta ect d ins ries with a sourceof power:and a primary control such as a gas. valve, an oil burnerrelay, a stoker control or a damper motor. The current drawn by suchdevices varies over a Wide range, even among controls of a certain type.Hence it has been the custom to match the heater to the de: vice beingcontrolled by the thermostat. This. requires the services of an expertwho must. be

provided with heatersof various resistancesthat may be selected andinstalledin the. thermostat as required. Other methods of correlatingthe heat suppliedby the heater and; th operating diiierential of thethermostat are to provide an adjustable heater, to adjust the. heattransfer between the heater and the. thermal element, or to vary thedifferential. In each of these methods knowledge of the problem involvedis essential in order to obtain optimum results.

It isan object of the present invention to provide an anticipatingthermostat that may be connected; to control various devices without thenecessity of matching the anticipating heater to the current drawn bysuch a device.

Another object of the invention is to provide a thermostat having ananticipating heater that is energized from a circuit that does notinclude the device being controlled.

Another objectis to. provide an electric clock thermostat having ananticipating heater that is energized from the clock circuit and iscontrolled by a switch actuated by the temperature responsive element.

A further object is to provide a clock thermolstat that may besubstituted for an existing thermostat without considering the exactvalue of the current that is to be controlled by the control contacts ofthe device.

A somewhat broader object is tov providea thermostat having anelectrically energized antic patin heate i h ch h on un io m y be otherthan control of n le t ic ircuit Other objectswill be apparent fromthewritten 3 of Figures 1-3 shown connected in a control system,

Figure is a diagrammatic view of the device of Figures 1-3 connected ina system utilizing two control circuits,

Figure 6 is another diagrammatic view of the device of Figures 1-3connected in still another control circuit,

Figure 7 is a diagrammatic view of an anticipating thermostat in whichthe control element is a pilot valve rather than an electric switch, and

Figure 8 is a diagrammatic view of another modification.

Control circuits are usually low voltage so that the cost of wiring isgreatly reduced and so that light duty switching devices may beemployed. Hence the usual line voltage is reduced by a transformer,usually to or volts. Also, to facilitate wiring, the motor of anelectric clock thermostat is usually selected to operate at low voltageand a separate transformer is used to supply the clock. While it wouldbe feasible to operate both the control circuit and the clock motor fromthe same transformer, this is seldom done since many devices controlledby room thermostats are provided with built in transformers that arecapable only of supplying enough power for their normal control functionand would not supply sufficient voltage if additionally loaded by aclock motor. Also in many installations a line voltage safety devicesuch as a limit control is wired in the supply circuit ahead of thetransformer. The clock motor could not be energized from the controlcircuit transformer in such a system since opening of the limit controlwould stop the clock.

In Figures 1, 2 and 3 of the drawing a clock thermostat is shown havinga base H) of suitable insulating material which is adapted to be securedto the wall of a room. The base I5 is provided with a pair of terminalscrews H and I2 that are adapted to be connected to a suitable source ofregulated frequency alternating current. Terminal I is connected throughelectrical conductors l3 and I4 to a terminal E5 of a synehronous clockmotor [6. The clock motor is not shown in detail as such motors are wellknown in the electric clock art. The motor 16 is provided with anotherterminal which is connected by a conductor l8 to a bracket I9. Thebracket I9 is connected by a wire 20 to a conducting washer 2| which isheld against the top of a cylindrical graphite heater 22 which is shownmost clearly in Figure 3. The lower portion of the graphite block 22rests against the top of a stud 23. The stud 23 lies in electricalconducting relation with a bracket 25 that is suitably secured to thebase Ii). A screw 26 passes through an insulating washer 21 and into thestud 23 to secure the washer 2| and heater 22 against stud 23. Thebracket 25 is connected by conductors 28 and 29 to the terminal screwl2. The conductor 28 is electrically connected to the bracket 25 by' ascrew 3| which aids in securing the bracket 25 to the base I0. Thus, itwill be seen that the clock motor l6 and the heater .22 are electricallyconnected in series circuit with the terminals H and I2.

The bracket 25 carries a pin33 at right angles to the base It]. Abracket 34 is pivotally mounted on the pin 33 and has a U-shaped bimetalthermostatic element suitably attached thereto. When the heater 22 isenergized and is raised to a temperature higher than ambient, heat willflow 4 from the heater through the stud 23, the bracket 25, the pin 33and the bracket 34 into the bimetal element 35.

The upper end of the right hand leg of the bimetal element 35 as seen inFigure 1 is positioned by a link 37 which is pivoted to the bimetalelement and also on a pin 38 carried by an arm 33 of the temperaturesetting mechanism. This mechanism is described in detail in theapplication of Carl G. Kronmiller Serial No. 2,230, filed January 14,1948, and will not be described in detail here. The arm 39 is, ineifect, one arm of a bell crank member pivoted on a pin 48 in the baseHi, the other arm 4| of which is provided with a pin 32 that extendsbetween a pair of control point adjusting arms 54 and 45. The arms 44and 45 are pivoted in the base H) on a suitable friction pivot andcooperate with an indicia plate 41 also secured to the base Ill. The pin42 will be in engagement with one or the other of the arms 54 or 55depending upon the position of a cam follower arm 48 which is alsopivoted on the pin 48. A strain release spring 49 acts between the bellcrank and a portion of the arm 48 so that the arms 39, 4| and 48 move asa unit unless the arm 48 is moved farther in a counterclockwisedirection than the arm 4| is permitted to move as determined by theposition of the setting arm 45.

The clock motor i5 drives a gear 5i which is the last of a series ofgears driven by the motor armature. A 24-hour dial 52 is secured to thegear 5| to rotate therewith and a cam 53 is adjustably secured to thegear 5! and the dial 52 to rotate therewith. The extent of the raisedportion of the cam 53 as well as its position relative to the dial 52may be adjusted as described in the aforementioned Kronmillerapplication. The raised portion of the cam 53 is adapted to engage aroller 55 carried by the end of the arm 48. When the raised portion ofthe cam 53 engages the roller 55 to move the arm 48 in acounterclockwise direction, the arms 4| and 39, the link 3?, and the topend of the righthand leg of the bimetal element 35 will be positioned asdetermined by the setting of the temperature setting arm 45. When thecam 53 is rotated so that the roller 55 is off the raised portion of thecam, the pin 42 carried by the arm 4| will be positioned by thetemperature setting arm 44, since the bimetal element 35 exerts aclockwise force on the link 31 and arm 39, as will appear below.

The bracket 25 which is secured to the base I0 is provided with anextension 50 to which is secured a flexible strip 5!. The upper end ofstrip 6| is bifurcated to form two separate resilient strips 62 and 63which carry movable contacts 64 and 65. A switch arm 67 is secured tothe strip 6| adjacent the bracket portion 60 but spaced slightlytherefrom. The switch arm 61 has an extension 63 that engages the upperend of the left-hand leg of the bimetal element 35. The strip BI ispreshaped so that the portion intermediate the bracket 60 and the switcharm 61 exerts a bias on the arm 61 in a clockwise direction that tendsto rotate the bimetal element 35 about the pin 33 in a clockwisedirection and to rotate the arms 39 and 4| of the temperature selectingmechanism to bring the pin 42 into engagement with the temperaturesetting arm 44. Thus, when the roller 55 is opposite the low portion ofthe cam 53 the assembly will be biased in a clockwise direction byassay-e7 the spring strip 6| toward the limiting position as determinedby the arm 44.

The upper portion of the switch arm 6'! lies adjacent a magnet I whichis carried on a spring strip 'II which in turn is secured to the baseIii. A bracket I2 overlies the strip and is provided with an upstandingportion I3 which carries the stationary contact I4 adapted to cooperatewith the movable contact 64. A screw 16 is adjustable in the bracketportion I3 and engages the back side of the magnet ID to adjustablyposition the magnet against the bias of the spring strip 'II. The upperend of the switch arm 6'1 is of magnetic material and acts as anarmature to cooperate withthe magnet I0. Adjustment of the magnet I0with respect to the stationary contact I4 serves to determine theoperating differential of the switching mechanism. The movable contact65 is adapted to engage a stationary contact '18 which is carried by abracket I9 that is secured to the base ID by ascrew 80. For a moredetailed description of certain phases of this switching mechanism,reference is made to Kronmiller Patent Re. 22,998 and to Kronmillerapplication Serial No. 681,461 filed July 5, 1946, now Patent 2,493,294.

The screw 80 also secures a bracket BI to the base I0, but the bracket8| is insulated from the bracket I9 by a washer 82. The bracket 86carries another stationary contact 84 that is adapted to engage amovable contact 35 which is also carried by the switch arm Bl. It willbe noted that the contacts 8485 will be in engagement only when themovable contacts 64 and 55 are out of engagement with the stationarycontacts I4 and I8. The bracket 8| also carries a magnet 81 that isadapted to cooperate with the extension 68 of the switch arm 67 which isof magnetic material and serves as an armature to assure positive actionof the contacts 8485. The resilience of the bimetal element 35 is reliedupon to cooperate with the magnets Ill and 8'! to assure that the switcharm 61 will snap between the position in which the, contacts 8465 are inengagement and the position in which the contacts 64 and 65 are inengagementwith the stationary contacts I4 and I8.

The stationary contact I8 is connected to a terminal screw 90 on thebase II! by means of the screw 80 and a conducting strip 91. Thestationary contact I4 is connected to the terminal strip 93 on the baseII) by means of the bracket portions I3 and "and by screws 94 and aconducting strip 95. The switch arm 61 and the movable contacts 64 and65 are connected by the spring strip BI to the bracket portion 60 andthrough the bracket 25 and the stud 23 through a conducting strip 91 toa terminal screw 98.

On a decrease in temperature from the position of the contacts shown inFigure 1, the bimetal element 35 will contract to reduce the distancebetween its two legs and to cause engagement of the contacts 64 and 65with the stationary contacts I4 and 1B. Thus a reduction in temperaturewill resultin the terminal screws 90, 93 and 98 being interconnected.

Since the heater 22 is connected to the stationary contact 84 throughthe washer 2!, conductor 20, and brackets I9 and 8|, and since the otherend of the heater 22 is connected to the movable contact 85 through thebracket 25, extension 60 thereof, and switch arm 61, an increase intemperature of the bimetal element 35 will cause engagement'of-thecontacts 84--85 to shunt the heater 22. Under this condition, a clockmotor I6 will be energized by a circuit from the terminal II, conductorsI3 and I4, motor terminals I5 and I1, conductor I8, brackets I3 and 8|,stationary contact 84, movable contact 85, switch arm 61, brackets 60and 25, screw 3| and conductors 28, and 29 to terminal I2. Thus it willbe seen that when the circuit is broken between the terminal screws 90,93 and 98 by disengagement of the movable contacts 64 and 65 fromstationary contacts I4 and I8 that the heater 22 will not be energizedbecause closure of contacts 84-435 completes a circuit shunting theheater.

Figure 4 shows a typical application of the device described above. Thedevice is shown diagrammatically, and for the sake of clarity the switcharm 67 has been omitted and the movable contacts 64 and are shown asbeing mounted directly on the bimetal element. Here the device is shownas being in control of a gasvalve IBI which controls the flow of gas toa furnace I02 that is adapted to heat the space in which the thermostatis located. The furnace I02 is equipped with a limit switch I03 that isadapted to open a circuit when the temperature in the furnace becomeshigher than a preselected safe value. Wires IE4 and I05 are connected toa suitable source of power and energize the primary of a step downtransformer I06 through the limit switch I03 and a conductor I01. A wireI35 connects one terminal of the secondary of the transformer I66 to thethermostat terminal 93, and the other secondary terminal is connected bya wire I69 to the gas valve IUI. A wire [I0 connects the other terminalof the gas valve to the thermostat terminal 98. Since the gas valve Ielrequires only a single control circuit, it is necessary only to use oneof the control circuits available in the thermostat. On a decrease inroom temperature the bimetal element 35 will deflect to cause engagementof the contacts 64-I4 and disengagement of the contacts 84-85. This willcomplete a circuit including the secondary of the transformer I66 andthe gas valve 10! to open the valve and heat the furnace I62. Thethermostat terminals II and I2 are connected by wires III and Hz to thesecondary of a transformer II3 which is energized by line wires I 14 andI I5. When the thermostat is satisfied and the contacts 84-85 are inengagement the anticipating heater 22 is shunted out of the circuit andthe motor I6 is energized through the contacts 84-35. However, whenthere is a call for heat and the contacts 84-85 are open, the heater 22is placed in series with the clock motor IE to supply artificial heat tothe bimetal element 35. The resistance of the heater 22 is relativelysmall compared to the effective resistance of the motor I6 and henceinclusion of the resistor 22 in series with the motor I6 does not reducethe voltage across the motor sufficiently to impair its operation.

Figure 5 is a diagrammatic illustration of a control circuit in whichboth sets of control contacts of the thermostat are utilized. Here thethermostat is shown in control of a burner motor I20 which eifectivelysupplies heat to a furnace or boiler which in turn supplies heat to thespace under control. The furnace or boiler is provided with a limitcontrol I2I of the type which includes two sets of contacts I22 and I23,the arrangement being such that on a rise in temperature the contactsI23 are opened before the contacts I22 in order to provide an operatingdifmostat.

ferential. The control circuit is energizedvv from they secondary of atransformer I25 which is supplied with current by wires I25 and I21. Theburner motor I25 is controlled by a relay I28 through relay contacts I29and wires I30, I3I and I32 which are connected to the supply wires I26and I27. When the limit control contacts I22 and I23 are closed, therelay I28 and hence the burner motor I29 will be under the control ofthe bimetal element 35 of the room thermostat. This circuit may betraced from the secondary of the transformer I25 through the limitcontrol contacts I22, a wire I34 to the thermostat terminal 55, thecontacts 33-65, contacts G4','I4', thermostat terminal 93, a wire I35 tothe limit control contacts I23, a wire I36 to the relay winding I3l andback to the secondary of the transformer :25. However, if the thermostatis calling for heat and the furnace becomes overheated the contacts ofthe limit control I21 will be opened. Opening of the limit controlcontacts I23 alone will not stop the burner since the relay I23 isprovided with holding contacts I33 which are connected by a wire I39 tothe terminal 93 of the room thermostat. This holding circuit may betraced from the secondary of the transformer I25 through the limitcontrol contacts I22, wire I34, thermostat contacts I8--55, element 35,thermostat terminal 33, wire I39, relay contacts I35, relay coil I3? andback to the transformer secondary. If the furnace temperature risessufficiently to open the limit control contacts I22, the relay I28 willbe deenergized and it will be necessary for the furnace temperature todrop sufiiciently to close limit control contact I23 as well as contactsI22 in order to reenergize the relay. The clock and anticipating heaterenergizing circuit of Figure 5 is identical to that described inconnection with Figure 4.

The thermostat connections as described in connection with Figures 4 and5 are particularly adapted for use when it is desired to substitute thedescribed clock thermostat for a conventional room thermostat. It isoften diiiicult to provide the additional wires necessary forenergization of the clock motor since the connecting wires for thethermostat are customarily concealed within the walls of the room. Toavoid the necessity for providing these additional wires, the wires IIIand II2 connecting with the terminals II and I2 may conveniently beembodied in a single flexible cord, and the transformer II3 may beattached to the end of the flexible cord and provided with prongsadapted for insertion in an ordinary wall outlet.

Figure 6 shows an arrangement adapted for use when three wires areavailable for connection to the thermostat. Here a controlled device I4!which may be a gas valve, relay or the like, is energized by thesecondary of a transformer I22 under the control of the room ther- Oneside of the secondary of the transformer 552 is connected to thethermostat terminal 55 by the wire M3 the device Isl is connected tothermostat terminal 55 by a wire IM. Closing of the contacts 55-i8completes the circuit to-energize the device I ii It will be appreciatedthat since fall in temperature in terconnects all three of thethermostat terminals til, 93 and as, that the wires I53 and I53 could beconnected to any two of these terminals. The clock motor I5 and theanticipating heater 22 are energized from the secondary of a trans-.former I45 through a wire I45 connected to the thermostat terminal IIand the wire I43 which is connected to the terminal 98. Since thethermostat terminals I2 and 98 are internally connected it will beapparent that this method of connecting the instrument is the equivalentof the hookups shown in Figure 4. Its advantage lies in cases where athree-wire concealed thermostat cable is already available, and wherethe device being controlled is adapted for energization by only twowires.

Figure '7 diagrammatically illustrates a modified form of clockthermostat. All of the operating parts of the device may be identical tothose described in connection with the instrument illustrated in Figures1, 2 and 3 with the exception that a pilot valve has been substitutedfor the control contacts. The pilot valve comprises a nozzle I55 whichis adapted to be closed by a pivoted flapper I5I when there is a callfor heat. The nozzle I55 is connected to a steam valve I52 by a pipeI53. Air under pressure is supplied through a restriction I52 to boththe nozzle I55 and the valve I52. The valve I52 is adapted to open onincreased air pressure as supplied by the pipe I53 to permit the flow ofsteam into a radiator I55. When the flapper I5I is out of engagementwith the nozzle E50 air will escape from the nozzle I50 faster than itis supplied through the restriction I54 and the valve I52 will beclosed. The clock motor I5 is energized through conductors I57 and I58which connect the motor directly across the terminals II and I2. Inaddition to actuating the flapper valve the bimetal element 35 alsocontrols contacts I59 which control energization of the anticipatingheater 22. It will be seen that when the pilot valve is closed to admitsteam to the radiator I55 that the anticipating heater 22 will also beenergized. In this modification of the invention, the anticipatingheater could be connected in series with the clock motor as in thepreviously described modification but here there is no additionalcomplication involved in having the contacts which control the heateractuated to closed position when the temperature of the bimetal elementis reduced.

Figure 8 shows an arrangement in which the internal wiring of thethermostat is modified somewhat. The operative parts may be as shown inFigures 1, 2 and 3 but no use is made of the contacts 84-85. Here theheater 22 is of relatively high resistance and is connected in parallelwith the clock motor I5 while the thermostat is calling for heat. Thecontacts 54-14 control the source of heat as described in connectionwith Figure 4. The upper end of the heater 22 is connected by a wire I55to the terminal screw II, and the terminal screw I2 is connected by awire I5I to stationary contact 78 which is engaged by movable contact 65to complete the heater circuit whenever the control circuit isenergized. This heater control arrangement is also adaptable tothree-wire control circuits of the type shown in Figure 5, in which casecontacts I55-18 would additionally perform a control circuit function.

In view of the above description various modifications of the inventionwill occur to those skilled in the art. Suitable modification of thedevice would provide cold anticipation desirable when a thermostat isused to control a re frigeration compressor or other source of cold. Inthat case it is necessary that the anticipating heater be energized whenthe thermostat is satisfled. The scope of the invention is to bedetermined only by the appended claims.

I claim as my invention:

1. In a control device, a base, a thermostat includin a temperatureresponsive element and controlling means on said base, a clock mechanismincluding an electric motor on said base, means actuated by said clockmechanism and influencing thermostat for adjusting the control point ofsaid thermostat at predetermined times, a pair of terminals on said baseconstructed and arranged for connection to a source of electric current,an electric heater thermally associated with said temperature responsiveelement for applying artifical heat thereto, electrical connectionsterminals, said motor and said heater, said connections being arrangedto provide continuous operation or said motor, and contacts actuated bysaid temperature responsive element, said contacts being interposed insaid electrical connections for intermittently effecting energization ofsaid heater.

2. In a. control device, a base, a hermostat including a temperatureresponsive element and control means on said base, an electric motor onsaid base, means actuated by said motor and influencing said thermostatto adjust the control point of thermostat, a pair of terminals on saidbase, an electric heater thermally associated with said temperatureresponsive element for ap plying artificial heat thereto, electricalconnections between said terminals, said motor said heater, and contactsin said connections actuated by said temperature responsive elementcontrolling energization of said heater, said electrical connectionsbeing arranged to provide continuous energization of said motor.

3. In a control device, a base, a thermostat including a thermal elementand a control element on said base, a clock mechanism including anelectric motor on said base, means actuated by said clock mechanism andinfluencing said thermostat to adjust said thermostat at predeterminedtimes, an electric heater thermally associated with said thermal elementfor applying artificial heat to said element, contacts actuated by saidthermal element, a pair of terminals on said base, said terminals beinadapted for connection to a source of current, and conductorsinterconnecting said terminals and said clock motor for continuousoperation thereof, additional conductors connecting said connections andheater to the clock energizing conductors in such a manner that saidcontacts control the energization of said heater.

4. In a thermostat, a base, a thermostatic element carried by said base,control means on said base adapted to be actuated by said element, asnap switch adapted to be actuated by said element, a pair of terminalson said base, an electric motor carried on said base, a linkage actuatedby said motor for varying the relation between said element, saidcontrol means and said switch, an electric heater in heat exchangerelation to said element, conductors connecting said motor and heater inseries circuit with said terminals, and conductors connecting saidswitch in parallel circuit with said heater.

5. In a thermostat, a base, a thermostatic element carried by said base,control means on said base adapted to be actuated by said element, asnap switch adapted to be actuated by said element to closed position onan increase in temperature, a pair of terminals on said base, anelectric motor carried on said base, a linkage actuated by said motorfor varying the relation between said element, said control means andsaid switch, an electric heater in heat exchange relation to saidelement, conductors connecting said motor and heater in series circuitwith said terminals, and conductors connecting said switch in parallelcircuit with said heater.

6. In a thermostat, a base, a thermostatic element carried by said base,a double pole snap switch actuated by said element to close two circuitson temperature fall, a single pole snap switch actuated by said elementto close on temperature increase, an electric motor on said base, alinkage connecting said motor and said element for adjusting saidelement on said base at predetermined times, an electric heater in heattransfer relation to said element, a pair of terminals on said base,conductors connecting said motor and said heater in series circuit withsaid terminals, and conductors connecting said single pole switch inparallel circuit with said heater.

7. In a thermostat, a base, a thermostatic element carried by said base,a first snap switch actuated by said element to closed position on adecrease in temperature, a second snap switch actuated by said elementto closed position on an increase in temperature, a pair of terminals onsaid base, conductors between said terminals and the contacts of saidfirst switch, an electric motor on said base, a linkage connecting saidmotor and said element for adjusting said element on said base, anelectric heater on said base, a second pair of terminals on said base,conductors connecting said motor and said heater in series circuit withsaid second pair of terminals, and conductors connecting said secondswitch in parallel circuit with said heater.

8. In a control device, a base, a thermostat on said base, anelectrically energized clock motor on said base, a linkageinterconnecting said motor and said thermostat for adjusting the controlpoint of said thermostat at a predetermined time, a resistance in heatexchange relation to said thermostat for supplying artificial heatthereto, a switch actuated by said thermostat, terminals on said baseadapted for connection to a source of electric current, and electricalconnections between said terminals and said motor for continuousenergization thereof, further electrical connections between thefirstnamed electrical connections and said resistance, said furtherelectrical connections including said switch, said switch being arrangedto control the energization of said resistance.

WILLIS H. GILLE.

REFERENCES CITED The following references are or" record in the file ofthis patent:

UNITED STATES PATENTS

